[Wasm] Add internal JsPrimitive annotation

Before external classes could only represent JS object types and are
type-checked with `instanceof`.
@JsPrimitive allows external classes to represent primitive types with
`typeof` checks.

libraries/stdlib/wasm/internal/kotlin/wasm/internal/JsInteropAnnotations.kt

@@ -0,0 +1,13 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.wasm.internal
+
+/**
+ * Annotated external classes correspond to JS primitive type.
+ * @param type is a result of JS `typeof` operator applied to this type.
+ */
+@Target(AnnotationTarget.CLASS)
+internal annotation class JsPrimitive(val type: String)